Dual fuel engines may use a liquid fuel or a combination of a liquid and a gaseous fuel. However, the quality of locally available gaseous fuel can vary from location to location. Such variances may be significant, for example, in unimproved locations, such as drilling sites located in remote locations where high quality gaseous fuel may be unavailable and to which liquid fuel may be expensive to transport. In many of these areas, unrefined or unpurified combustible gaseous fuel from an oil or natural gas well may be readily available. In conventional dual fuel internal combustion engines, a general procedure involves measuring the quality of the locally available gaseous fuel and manually adjusting or calibrating the internal combustion engine to provide a proper ratio of gaseous fuel to liquid fuel or an amount of gaseous fuel to be substituted for liquid fuel based on (i.e., in response to) the quality of the locally available gaseous fuel. Fuel quality may include, for example, a heating value or energy content of the gaseous fuel per unit volume, the methane number (which is an indication of the anti-knock properties of the gaseous fuel), and/or the like.